1. Field of the Invention
This invention relates generally to a torsional spring for use in exercise equipment and, more particularly, to a torsional spring formed from a plurality of elastomeric spokes connected between an outer cylinder and a rotatable central hub.
2. Description of the Related Art
Designers have long attempted to produce exercise equipment that has the advantages of being lightweight and portable in design, but still requires extensive physical exertion, so as to emulate heavy weight systems. For example, it has been common for designers to replace heavy weights with frictional devices to controllably resist movement by a user. One example of such a frictional device is illustrated in U.S. Pat. No. 4,647,041 issued Mar. 3, 1987 to Neville C. Whiteley. In that device, increased resistance to movement is generated by increasing the force tending to hold a pair of surface engaging plates together.
Alternatively, other prior art devices have suggested the use of a spring mechanism to provide the desired resistance to movement by a user of the device. For example, U.S. Pat. No. 3,752,475 issued Aug. 4, 1973 to Arnold C. Ott discloses an exercise wheel that is rotatable about an axle and has a spring means operatively associated with the wheel and axle for increasing resistance to rotation of the wheel relative to the axle. Several embodiments of the spring means are illustrated, including a series of resilient elements, such as rubber bands. The rubber bands are connected between the wheel and the axle so that as the wheel rotates about the axle the rubber bands are stretched and wrapped around the axle. The stretching rubber bands exhibit increasing resistance to movement of the wheel so that a user must exhibit considerable force to rotate the wheel. However, rubber bands suffer from the inherent disadvantage that, owing to their repeated exposure to high stress, they have a relatively short fatigue life and are in need of frequent repair and replacement.
More specifically, as the wheel is rotated relative to the axle, the rubber bands are stretched and wrapped about the axle. The first portions of the rubber bands that are in actual contact with the axle cease to stretch when they come in contact with the axle. These first portions of the rubber bands are, therefore, subject to a relatively small amount of strain. The second portions of the rubber bands that are not in contact with the axle continue to stretch and are subject to substantially higher amounts of strain. Thus, since the fatigue life of the rubber band is directly related to the peak strain, the second portions of the rubber bands have a relatively shorter fatigue life than the first portions of the rubber bands. The overall fatigue life of the rubber bands is, of course, determined by the relatively short fatigue life of the second portion.
The present invention is directed to overcoming one or more of the problems set forth above.